Alpha chooses only 1.d4 and 1.Nf3, while Stockfish goes for 1.e4
Judging from this, I can say that Alpha is much weaker than SF in terms of software, and the only reason for the win is the very big hardware advantage.

I think Table 2 [ECO opennings] in the PDF would answer your argument.
All those 12 common opennings (on that Table 2) was played by AlphaZero against SF8, 100 times each. and only a total of 4 losses (out of 300 games) as white starting with 1.e4 (for AlphaZero) as shown on that table.